class Solution {
public:
    int waysToStep(int n)
    {
        if (n <= 2) return n;
        vector<int> dp(n + 1);
        dp[0] = 0;
        dp[1] = 1; dp[2] = 2; dp[3] = 4;
        for (int i = 4; i <= n; i++)
        {
            dp[i] = ((dp[i - 1] + dp[i - 2]) % 1000000007 + dp[i - 3]) % 1000000007;
        }
        return dp[n];
    }
};